1. The Field of the Invention
The invention is directed to an apparatus for gauging work pieces. More specifically the invention is directed toward non-contact gauging of work pieces during surface profile altering operations.
2. The Background Art
In manufacturing nominally circular parts it is necessary to make accurate quality assessments of the parts before, during, and after the manufacturing process. Such parts are often termed workpieces or rolls and are configured such that at least a portion of the part has a nominally circular geometric shape. Such workpieces may have the shape of a cylinder, cone, or have circularly symmetric parts of irregular axial cross section. A workpiece may have a crown portion, a concave portion, or a multiplicity of both. Workpieces range in sizes from two inches in diameter to several feet in diameter depending on the function or application of the workpiece. Workpieces have a wide variety of uses including use in rotating machinery such as in assembly line machinery or in turbines used in power generation or propulsion. In turbine applications, workpieces are used for cumbusters, turbine rotors, and turbine casings.
A workpiece is machined by applying a grinding wheel to a workpiece which is rotating about the longitudinal axis of the workpiece. The grinding wheel acts to reduce material on the workpiece to alter the surface and achieve a desired diameter. The grinding wheel is applied at different locations along the longitudinal axis of the workpiece to provide diameters dependent on the longitudinal position of the workpiece. In this manner, a workpiece is created with a specific shape. During grinding, a coolant or working fluid is applied to the workpiece to reduce heat damage to the workpiece due to frictional heat resulting from application of the grinding wheel.
For quality control and assessment, it is required in the fabrication process to accurately measure the diameters of the workpiece along a longitudinal axis of the workpiece. Diameter measurements of a workpiece provide direct information about the dimensions of the workpiece. Before machining a workpiece, it is necessary to perform diameter measurements in order to accurately apply the grinding wheel to obtain the desired results. During the machining process, it is necessary to conduct precision measurements to determine the current diameters to know when the desired shape has been achieved. Finally, after the machining process it is desirable to measure the shape of the workpiece as a record and to ensure quality control of the process.
Diameter measurements have been conventionally performed through the use of micrometers or calipers that encircle the workpiece so as to come into contact with opposite side surfaces of the workpiece. This process is difficult and time consuming in that it delays machining of the workpiece and requires the expertise of a skilled operator performing the measurement. Since mechanical surface contact is required for micrometers and calipers to work, slight fluctuations in surface texture introduce error in measurement. The operator of the micrometers of calipers must also be experienced with them in order to obtain accurate and repeatable measurements.
During grinding operations, contact gauges such as micrometers and calipers are in contact with the surface of the workpiece, to measure the workpiece diameter as it is being machined. The contact between the caliper and the roll results in wear and vibrations which limit the caliper's life. This limits the accuracy of the readings which in turn limits the accuracy of the grinding process. Further, the contours of the workpiece may make contact gauging instruments impossible to use due to the lack of positive engagement between the contacting surfaces of the instruments with the workpieces. A further disadvantage is that contact with the workpiece creates undue wear on the workpiece which cause deformities in the workpiece.
More sophisticated measurement methods suggest the use of non-contact gauging but often require elaborate systems employing several non-contact gauges to perform measurements. Non-contact gauging systems are fairly expensive in requiring several non-contact gauges which must operate in computer controlled operation with one another. Non-contact gauging systems often require substantial delays in setting up in order to provide accurate measurements. Such systems may further require experienced operators to provide accurate placement of the non-contact gauges and to correctly interpret the results. Non-contact gauging systems often do not disclose how the non-contact gauge is initially positioned relative to workpieces of various sizes and how working fluids are prevented from interfering with the measurements.
Several non-contact gauging systems incorporate conventional laser sensors and use a system of lenses and mirrors in the path of the laser beam. Lenses and mirrors have inherent imperfections and the resulting measurements will be in error to the extent of the imperfections. These imperfections result when the mirrors or lenses are placed between the laser light source and the workpiece. When the beam reflects from a mirror or passes through a lens, the beam takes a path which is altered from its ideal path. This is due to the imperfections inherent in all lenses and mirrors. The imperfectly directed beam can strike the workpiece when it should pass by and be detected. This leads to the computer calculating a measurement based on a false edge of the workpiece. When these imperfections are introduced in the path of the beam prior to the beam contacting the object being measured, significant error is introduced into the measuring device.
Thus, it would be an advancement in the art to provide a non-contact gauging system for use in surface profile altering devices for precision machining of workpieces. It would be an additional advancement in the art to provide a non-contact gauging system which can be rapidly and accurately positioned for reliable, nondestructive, and accurate measurements. It would be a further advancement in the art to provide a non-contact gauging system which is relatively inexpensive to perform measurements before, during, and after the process of machining a workpiece to provide dimensions of the workpiece.